1. Technical Field
The present invention relates to a vibratory structure made of, for example, a crystal or the like, a vibrator including this vibratory structure, an oscillator provided with this vibrator, and an electronic apparatus.
2. Related Art
Conventionally, a quartz crystal vibrator functioning as a frequency control element is adopted for an oscillation circuit provided in various electronic apparatuses.
Specifically, a tuning-fork type quartz crystal vibrator is used as a quartz crystal vibrator that is downsized, break-proof, and that accurately vibrates at a low electric power.
In the above-described tuning-fork type quartz crystal vibrator, the number of vibrations, that is the frequency, is mainly determined by the length and the width of an arm of a quartz crystal vibratory element.
Specifically, the above-described tuning-fork type vibrator for functioning as a clock source is incorporated together with an oscillation circuit into various electronic apparatuses such as a clock.
In recent years, in conjunction with the downsizing of various electronic apparatuses, a tuning-fork type vibrator of a small size has become required.
As a foregoing downsized tuning-fork type vibrator, the tuning-fork type quartz crystal vibrator including the structure which has a couple of vibratory arm sections and in which grooves are formed on the main face of each of the vibratory arm sections and drive efficiency of the quartz crystal vibratory element is improved is known.
FIG. 15 is a plan view illustrating a conventional example of a tuning-fork type vibrator.
This tuning-fork type vibrator is constituted by a crystal substrate of a Z-plate (Z-cut) in which a main face is orthogonal to the z-axis of crystal axes (xyz).
A couple of vibratory arm sections 12 and 13 are formed so as to extend from a base 11.
Here, with regard to crystal axes (xyz) in the tuning-fork type vibrator, the x-axis direction corresponds to the width (W), the y-axis direction corresponds to the length (L), and the z-axis direction corresponds to the thickness (D).
FIG. 16 is a cross-sectional view illustrating the conventional example of the tuning-fork type vibrator taken along the line C-C shown in FIG. 15.
As shown in FIG. 16, in each of the vibratory arm sections 12 and 13, grooves 12a and 13a are formed on the main faces (face perpendicular to the z-axis direction), and grooves 12b and 13b are formed on the back faces.
In addition, as shown in FIG. 16, drive electrodes are formed on the groove and a side face of each of the vibratory arm sections 12b and 13b so as to drive the vibratory arm sections 12b and 13b. 
In each of the vibratory arm sections 12b and 13b, the drive electrode 14a is formed in the groove 12a and the drive electrode 14b is formed in the groove 12b. The drive electrodes 14c and 14d are formed on both side faces of the vibratory arm section 12.
The drive electrode 15a is formed in the groove 13a and the drive electrode 15b is formed in the groove 13b. The drive electrodes 15c and 15d are formed on both sides of the vibratory arm section 13.
Here, the side faces of the vibratory arm section 12 and the sides of the vibratory arm section 13 are the faces that are orthogonal to the x-axis direction.
In addition, in each of the vibratory arm sections 12b and 13b, the vibratory arm sections 12b and 13b are wire-connected to each other so that a drive-voltage with a coordinate phase is supplied to the drive electrodes 14a, 14b, 15c, and 15d, and a drive-voltage with an opposite phase related to the foregoing electrodes is supplied to the drive electrodes 14c, 14d, 15a, and 15b. 
As a result, in each of the vibratory arm sections 12b and 13b, inflection vibration is generated by the electrical field generated between the main faces and the side faces in forward/backward directions, and the tuning fork is thereby vibrated.
For example, in the vibratory arm section 12, by supplying the electrical field in the x-axis direction from an inner periphery face of the groove to both side faces, when the left side portion shown in FIG. 16 is extended in the y-axis direction, the right side portion is contracted, and the vibratory arm section 12 is thereby displaced toward the vibratory arm section 13 in a direction in which the vibratory arm sections 12 and 13 face each other.
In contrast, in the vibratory arm section 13, by supplying the electrical field in the x-axis direction from both side faces to the inner periphery face of the groove, when the left side portion shown in FIG. 16 is contracted in the y-axis direction, the right side portion is extended, and the vibratory arm section 13 is thereby displaced toward the vibratory arm section 12 in a direction in which the vibratory arm sections 12 and 13 face each other.
In addition, by supplying voltage to each electrode so as to generate the electrical field in an opposite direction relative to the above-described case, the vibratory arm sections 12b and 13b vibrate in a direction in which the vibratory arm sections 12b and 13b are drawn apart from each other. Therefore, the vibratory arm sections 12b and 13b are vibrated in a retrorse horizontal direction, and the tuning fork is thereby vibrated.
As shown in FIG. 17A, normal vibration in the horizontal direction (x-axis direction) indicated by arrow B of the drawing is generated when the width W is comparatively great and the thickness D is comparatively low in the vibratory arm sections 12b and 13b. 
However, if the width W is less than or equal to 1.2 times the thickness D, a vertical component that is vibration component in the direction indicated by arrow C is added in, the vibration in the direction indicated by arrow E as shown in FIG. 17B is thereby generated.
When the vibration component in the direction indicated by arrow C communicates to the base, energy (vibration energy) is lost in an adhesive or the like disposed on the fixed region of base 11 at which the vibratory element shown in FIG. 15 is fixed to a package or the like.
Therefore, the vibration by vibratory arm sections 12b and 13b may lack stability caused by variations in the fixation strength of the vibratory element.
Consequently, there is a problem in that variations in the CI (crystal impedance) values of mass-produced vibratory elements increase.
Therefore, as shown in FIG. 15, in the base 11 including a side face 11r from which the vibratory arm sections 12b and 13b are extended, and side faces 11q that makes an angle together with the side face 11r and comes in contact with the angle, the structure in which an incision 16 is formed on the side faces 11q is proposed.
In the tuning-fork type vibrator including the structure having the incision 16, it is possible to prevent the vibration of the vibratory arm section from leaking out toward the base 11.
This tuning-fork type vibrator is disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 2004-62134.
As a result, by the above-described structure, it is possible to downsize the base 11 while the CI value is maintained, downsize whole vibratory element, and reduce variations in the CI values of mass-produced vibratory elements.
In the vibratory element disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-62134, the frequency is determined by the ratio between the width of the vibratory arm section and the length of the vibratory arm section (f∝W/L2).
However, in the case of attempting to further downsize the vibratory element, the width of the vibratory arm section is extremely small, and it is thereby difficult to form a groove with a stabilized shape.
Therefore, the intensity of electrical field supplied to a crystal section is variable, oscillation characteristics become unstable, and one of or all of characteristic values such as a CI value, a Q value, the capacitor ratio, or the like become degraded.